It's up to the device. There are no requirements as to which message gets sent first. There could also be other messages pending as well, for example someone could have changed the DMX Start Address on the menu of the device so it Queued up a message to report that back to the console as well.

Put another way, the controller should never make an assumption that just because it got an ACK_TIMER earlier that when it does the next GET QUEUED_MESSAGE that it would get a response back for a specific PID.